1. Field of the Invention
The present invention relates to a method of manufacturing a stamper that is used for manufacturing a light guiding plate to be utilized for a liquid crystal display or the like.
2. Description of the Related Art
A liquid crystal display to be used for a word processor, a personal computer, a thin type television or the like usually comprises a rear-illuminating device. Most rear-illuminating devices use a light guiding plate of an edge light type. The light guiding plate of the edge light type is a transparent plate-shaped member and has an element for changing the angle of light transmitted through the light guiding plate or the angle of light reflected by the light guiding plate (which will be hereinafter referred to as a xe2x80x9cdeflecting elementxe2x80x9d). At least one of side surfaces of the light guiding plate serves as a light incident plane, and the light incident plane is provided with a light source having a tube shape or the like. The light emitted from the light source is incident through the light incident plane and is reciprocated and propagated between the upper and lower surfaces of the light guiding plate. At this time, the light having the direction changed by the deflecting element is emitted through the upper surface of the light guiding plate as illuminating light for the rear-illuminating device. Accordingly, the upper surface of the light guiding plate becomes a light emitting plane and the density distribution of the deflecting element and the shape of the deflecting element are predetermined such that the luminance of the light emitted from the light-emitting plane is uniform over the whole light emitting plane.
For the deflecting element, there are used (1) a white ink for scattering or reflecting light which is applied onto the surface of the light guiding plate, (2) a portion of projections and depressions for scattering or reflecting light which is formed on the surface of the light guiding plate, (3) light diffusing particles dispersed in the light guiding plate and the like.
In the case of the type (1), the white ink is applied by the method of screen-printing or the like. When the thickness of the white ink in a printed surface is nonuniform, a distribution is generated in the ability of the light reflection of the deflecting element. As a result, the luminance of the light emitted from the light-emitting plane of the light guiding plate becomes nonuniform. Furthermore, if dust in the air is mixed into the white ink or sticks onto the printed surface during the printing work, the light is scattered by the dust so that the uniformity of the luminance cannot be obtained. In the case of the type (3), even if the light guiding plate is to contain the deflecting element to obtain a predetermined density distribution, it is hard to disperse the light-diffusing particles into a base material with the predetermined density distribution.
For the above-mentioned reasons, the rear-illuminating device of many liquid crystal displays uses the light guiding plate of the above type (2), which includes, as a deflecting element, a portion of projections and depressions by which the light is diffused or reflected over a surface. For example, U.S. Pat. No. 5,961,198 has described a light guiding plate having a portion of projections and depressions as a deflecting element. Moreover, U.S. Pat. No. 5,776,636 has disclosed a method of manufacturing a light guiding plate including a portion of projections and depressions as the deflecting element.
Referring to FIGS. 2A to 2H, a brief description will be given to the procedure for manufacturing a light guiding plate having convex dots as a deflecting element using the method of manufacturing a light guiding plate described in the U.S. Pat. No. 5,776,636. A glass substrate 21 (FIG. 2A) has one of surfaces mirror polished and washed. A positive type photoresist is applied onto the polished surface of the glass substrate 21 by spin coating or the like, thereby forming a photoresist layer 22 (FIG. 2B). A photomask 23 being described a pattern corresponding to a plurality of dots of the light guiding plate (which will be hereinafter referred to as a xe2x80x9cdot patternxe2x80x9d) is provided on the photoresist layer 22, and the photoresist layer 22 is exposed through the photomask 23 (FIG. 2C). In the photomask 23, light is not transmitted through a portion corresponding to a convex dot pattern in the light guiding plate but is transmitted through a portion corresponding to a concave region between the dots in the light guiding plate. The photoresist layer 22 is exposed through the photomask 23, and a developer develops thus exposed photoresist layer 22 (FIG. 2D). Consequently, the region (exposed portion 24) in the photoresist layer 22 which has been exposed at the exposing step of FIG. 2C is removed and an unexposed portion 25 remains on the glass substrate 21.
An electric conductive film 26 is formed by vapor deposition, sputtering or the like over the whole upper surface of the glass substrate 21 on which the unexposed portion 25 of the photoresist layer 22 is provided (FIG. 2E). Then, the electric conductive film 26 is used as an electrode to form an electroforming body 27 by electroforming (FIG. 2F). Thereafter, the outer periphery is processed if necessary. Consequently, a stamper 28 including the electric conductive film 26 and the electroforming body 27 can be manufactured (FIG. 2G).
By using the stamper 28 as a mold, a resin is subjected to injection molding. Consequently, a light guiding plate 29 having a desirable dot pattern can be manufactured (FIG. 2H).
Moreover, Japanese Laid-Open Patent Publication No. Hei 4-259938 (1992/259938) has disclosed a method of manufacturing a stamper for manufacturing an information recording medium having a prepit such as a compact disk. The Japanese Laid-Open Patent Publication No. Hei 4-259938 (1992/259938) has disclosed a method manufacturing a stamper in which a silicon wafer or a metal plate is used as a substrate, and a photoresist layer is formed on the substrate of the silicon wafer or the metal plate to expose and develop a pattern and the substrate is subjected to dry etching by using the developed photoresist layer as a mask member so that a mother substrate having a concave portion formed thereon corresponding to a pre-formed pit pattern is obtained on the substrate of the silicon wafer or the metal plate. The mother substrate is thereafter subjected to the electroforming to obtain a stamper.
In the method of manufacturing a stamper described in the U.S. Pat. No. 5,776,636, the electroforming body 27 constitutes most parts of the stamper 28. For this reason, the thickness of the electroforming body 27 should be approximately 0.1 to 0.5 mm in order to obtain a mechanical strength required for the stamper 28 that is used for the injection molding. Consequently, there is a problem in that a long time is taken to the electroforming step for forming the electroforming body 27 and a manufacturing cost is increased. For example, in order to form the electroforming body 27 having a diameter of 200 mm and a thickness of 0.3 mm, a time required for electroforming is one hour or more. In order to manufacture a stamper for a light guiding plate for a large-sized liquid crystal display having a diagonal of 15 inches, a disk-shaped glass substrate having a diameter of 500 mm is to be used as the glass substrate 21. In this case, four hours or more are required for electroforming to obtain the electroforming body 27 having a thickness of 0.3 mm.
In the method of manufacturing a stamper for an information recording medium which has been disclosed in the Japanese Laid-Open Patent Publication No. Hei 4-259938 (1992/259938), a silicon wafer or metal plate having a large area is used for a substrate and a large-sized dry etching device is required for etching the substrate. Consequently, an equipment cost is increased.
In order to solve the above-mentioned problems, it is an object of the present invention to provide a stamper manufacturing method that does not require special equipment such as a dry etching device and further it is possible to shorten a time taken for manufacturing a stamper.
In order to attain the above-mentioned object, the present invention provides the following stamper manufacturing method.
More specifically, there is provided a method of manufacturing a stamper, comprising:
a forming step for forming a photoresist layer on one of surfaces of a substrate having electric conductivity;
an exposing step for exposing a desirable portion of the photoresist layer;
a developing step for developing the photoresist layer;
an electroforming step for forming an electroforming body on a portion, where the photoresist layer having been removed at the developing step, of the substrate; and
a washing step for carrying out washing to remove the photoresist layer from the substrate.